System, apparatus, and method for grafting tissue

ABSTRACT

Systems, apparatus, and methods may be adapted for grafting tissue at a tissue site that may include an elongate housing and a plurality of elongate cutting members. The plurality of elongate cutting members may define a cutting surface at a distal end of the elongate housing. The cutting surface may be adapted to contract from a first diameter to a second diameter that is less than the first diameter. The contraction of the cutting surface from the first diameter to the second diameter may define a tapered profile between the first diameter and the second diameter suitable for obtaining a tapered graft.

RELATED APPLICATION

This application claims the benefit, under 35 USC § 119(e), of U.S.Provisional Patent Application Ser. No. 61/735,456, entitled “System,Apparatus, and Method for Grafting Tissue,” filed Dec. 10, 2012, whichis incorporated herein by reference for all purposes.

BACKGROUND 1. Field

This specification relates generally to systems, apparatus, and methodsadapted for grafting tissue at a tissue site. The systems, apparatus,and methods may be suitable, for example, for performing osteochondralallografts, autografts, and grafts with other tissue types.

2. Discussion

Common usages for tissue grafts may include the treatment of cartilagedefects. For example, an osteochondral allograft (OCA) is a type oftissue graft commonly used to treat cartilage defects resulting fromosteochondrosis, trauma, and osteoarthritis. Current OCA techniques mayutilize cylindrically shaped grafts having a straight longitudinalsidewall that are inserted into a similarly shaped cylindrical cavity orsocket and held in place with a press-fit interface. The insertion ofthe cylindrically shaped graft may require large insertion forces toovercome the frictional resistance between the sidewall of thecylindrical graft and a sidewall of the corresponding cylindricalcavity. Installation of the graft may require mechanical impacting.Studies have shown that such mechanical insertion techniques maynegatively impact chondrocyte viability in the grafts and long termoutcomes of the procedure.

SUMMARY

The disclosed systems, apparatus, and methods may be adapted, in part,to decrease insertion force and energy required to achieve installationof grafts to overcome the problems associated with conventionaltechnologies and methods.

In some illustrative embodiments, a cutting apparatus for providing atapered tissue graft may include an annular cutting surface that may beadapted to contract from a first diameter to a second diameter that isless than the first diameter.

In other illustrative embodiments, a cutting apparatus for providing atapered tissue graft may include an elongate housing and a plurality ofelongate cutting members. The elongate housing may have a proximal end,a distal end, and a bore defining a longitudinal axis. The elongatecutting members may define an annular cutting surface at the distal endof the elongate housing. The annular cutting surface may be adapted tocontract from a first diameter to a second diameter that is less thanthe first diameter. The contraction of the annular cutting surface fromthe first diameter to the second diameter may define a tapered profilebetween the first diameter and the second diameter.

In some illustrative embodiments, a system adapted for grafting tissueat a tissue site, may include an elongate housing, a plurality ofelongate cutting members, and a plunger. The elongate housing may have aproximal end, a distal end, and a bore defining a longitudinal axis. Theplurality of elongate cutting members may extend lengthwise at thedistal end of the elongate housing, and may be positioned about thelongitudinal axis of the elongate housing. The elongate cutting membersmay define an annular cutting surface adapted to contract from a firstdiameter to a second diameter that is less than the first diameter. Thecontraction of the annular cutting surface from the first diameter tothe second diameter may define a tapered profile between the firstdiameter and the second diameter. The plunger may have an externalsurface and may be slidably disposed in the bore of the elongatehousing. When the annular cutting surface has the first diameter, theelongate cutting members may be biased against the external surface ofthe plunger at the distal end of the elongate housing.

In some illustrative embodiments, a method of grafting tissue at atissue site may include inserting a tapered graft tissue into acorresponding tapered socket at the tissue site.

In other illustrative embodiments, a method of grafting tissue at atissue site may include obtaining a tapered graft tissue having aninsertion end and an exposed end separated by a length. The taperedgraft tissue may have a first diameter at the exposed end that is largerthan a second diameter at the insertion end. The length between thefirst diameter and the second diameter may define an external taper. Themethod may additionally include preparing a tapered socket in the tissuesite for receiving the tapered graft tissue. The tapered socket maydefine an internal taper that substantially corresponds to the externaltaper of the tapered graft tissue. The method may also include insertingthe tapered graft tissue into the tapered socket.

In other illustrative embodiments, a method of grafting tissue at atissue site may include providing a cutting apparatus comprising anelongate housing, a plurality of elongate cutting members, and aplunger. The elongate housing may have a proximal end, a distal end, anda bore defining a longitudinal axis. The plurality of elongate cuttingmembers may extend lengthwise at the distal end of the elongate housing,and may be positioned about the longitudinal axis of the elongatehousing. The elongate cutting members may define an annular cuttingsurface that may be adapted to contract from a first diameter to asecond diameter that is less than the first diameter. The contraction ofthe annular cutting surface from the first diameter to the seconddiameter may define a tapered profile between the first diameter and thesecond diameter. The plunger may have an external surface, and may beslidably disposed in the bore of the elongate housing. When the annularcutting surface has the first diameter, the elongate cutting members maybe biased against the external surface of the plunger at the distal endof the elongate housing. The method may additionally include positioningthe plunger at the distal end of the elongate housing to place theannular cutting surface in the first diameter, and inserting the annularcutting surface longitudinally into a donor tissue source. Further, themethod may include displacing the plunger toward the proximal end of theelongate housing with donor tissue entering the bore of the elongatehousing as the annular cutting surface advances into the donor tissuesource. Additionally, the method may include obtaining a tapered grafttissue having an external taper by contracting the annular cuttingsurface from the first diameter to the second diameter along the taperedprofile as the plunger is displaced. Further, the method may includereaming a tapered socket in the tissue site for receiving the taperedgraft tissue. The tapered socket may define an internal taper thatsubstantially corresponds to the external taper of the tapered grafttissue. The method may also include inserting the tapered graft tissueinto the tapered socket.

In some illustrative embodiments, provided is a tapered graft tissue forinserting in a tapered socket. The tapered graft tissue may include aninsertion end and an exposed end separated by a length. The taperedgraft tissue may have a first diameter at the exposed end that is largerthan a second diameter at the insertion end. The length between thefirst diameter and the second diameter may define an external taper.

Other objects, features, and advantages of the illustrative embodimentswill become apparent with reference to the drawings and detaileddescription that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an illustrative embodiment of a cuttingapparatus for grafting tissue at a tissue site depicting a plungerpositioned toward a distal end of an elongate housing and an annularcutting surface positioned in a first diameter;

FIG. 1B is a perspective view of the cutting apparatus of FIG. 1A,depicting the plunger positioned toward a proximal end of the elongatehousing and the annular cutting surface positioned in a second diameter;

FIG. 2 is a top view of a proximal end of an illustrative embodiment ofa cutting apparatus for grafting tissue at a tissue site, depicting aplunger guide rod received within an arbor coupled to an elongatehousing;

FIG. 3 is a perspective view of an illustrative embodiment of a cuttingapparatus for grafting tissue at a tissue site including an annularcutting surface having serrations;

FIG. 4 is a perspective view of an illustrative embodiment of a cuttingapparatus for grafting tissue at a tissue site including a smoothannular cutting surface;

FIG. 5A is a perspective view of an illustrative embodiment of a taperedreamer;

FIG. 5B is a perspective view of a reamer guide pin suitable for usewith the tapered reamer of FIG. 5A;

FIG. 6 is a perspective view of a an illustrative embodiment of atapered graft tissue and an illustrative embodiment of a correspondingtapered socket in a tissue site;

FIGS. 7A-7E illustrate experimental results of cell viabilityrepresentative on day zero and day three for both a prior artcylindrical graft and a tapered graft tissue according to thisdisclosure;

FIGS. 8A-8C illustrate experimental results of cell death for both aprior art cylindrical graft and a tapered graft tissue according to thisdisclosure;

FIGS. 9A-9C illustrate experimental results of insertion force,insertion energy, and extraction force for both a prior art cylindricalgraft and a tapered graft tissue according to this disclosure;

FIGS. 10A-10B illustrate experimental results of insertion energy andextraction force for both a 20 millimeter diameter prior art cylindricalgraft and a 20 millimeter diameter tapered graft tissue according tothis disclosure; and

FIG. 11 provides an illustrative embodiment of a plunger that mayinclude an external surface rotatable about a tissue contact surface.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that depict non-limiting illustrative embodimentsfor practicing the subject matter disclosed in this specification. Otherembodiments may be utilized and logical, structural, mechanical,electrical, and chemical changes may be made without departing from thescope of this specification. To avoid detail not necessary to enablethose skilled in the art to practice the subject matter disclosedherein, the description may omit certain information known to thoseskilled in the art. Therefore, the following detailed description isprovided without limitation, and with the scope of the illustrativeembodiments being defined by the appended claims.

This specification relates to systems, apparatus, and methods that maybe adapted to provide a tissue graft having a tapered external surfaceand a corresponding internally tapered socket in a tissue site forreceiving the tissue graft. The disclosed systems, apparatus, andmethods may reduce the forces required to implant the tapered tissuegraft in the tapered socket while attaining the desired stability forgraft healing and incorporation. The benefits may include increasedchondrocyte viability and an increase in likelihood of success for thegrafting procedure.

Referring to FIGS. 1-6, provided is a system 102 that may be adapted forgrafting tissue at a tissue site 104. The system 102 may comprise acutting apparatus 106 for cutting a tapered graft tissue 108. Thecutting apparatus 106 may include an elongate housing 112 and aplurality of elongate cutting members 114. The cutting apparatus 106 mayadditionally include a plunger 116 that may be adapted to actuate theelongate cutting members 114 as described below.

Referring to FIGS. 1A-4, the elongate housing 112 may have a proximalend 120, a distal end 122, and a bore 124 defining a longitudinal axis126. The bore 124 of the elongate housing 112 may have a substantiallyconstant internal diameter 128 along a length 130 of the elongatehousing 112. The elongate housing 112 may include optional features,such as, for example, grasping handles 134 and an arbor 136. Thegrasping handles 134 may be positioned near the proximal end 120 of theelongate housing 112 to provide stability during operation. The arbor136 may be adapted, without limitation, to facilitate operation of thesystem 102 in combination with a desired surgical implement. Theoperation of the system 102 will be described in further detail below.

The arbor 136 may be positioned at the proximal end 120 of the elongatehousing 112 and may be substantially aligned with the longitudinal axis126 of the elongate housing 112. For example, the arbor 136 may besubstantially concentric to the longitudinal axis 126 and the bore 124of the elongate housing 112. In some embodiments, as depicted in FIGS.2-3, the arbor 136 may be adapted to couple the elongate housing 112 toa surgical implement, such as a drill. For example, the arbor 136 mayhave an octagonal cross-section or other shape having flat surfaces 140or keyways disposed about a circumferential surface 142 or perimeter ofthe arbor 136, to provide grip for the surgical implement. The arbor 136may also provide an impact surface 144 at the proximal end 120 of theelongate housing 112 adapted to receive blows from, for example, ahammer or similar instrument. In some embodiments, as depicted in FIG.4, the impact surface 144 of the arbor 136 may be a portion of increasedsurface area on the proximal end 120 of the elongate housing 112. Inother embodiments, the impact surface 144 may be separate from the arbor136. The arbor 136 may include an aperture 146 that may be substantiallyaligned with or concentric to the longitudinal axis 126 of the elongatehousing 112 for use in guiding the plunger 116 as described below.

Continuing with FIGS. 1A-4, the elongate housing 112 may have a circularcross section, and may be, for example, a tube formed of stainlesssteel, titanium, or similar material. The internal diameter 128 ordimension of the bore 124 of the elongate housing 112 may be, forexample, between about 3 millimeters to about 30 millimeters. Further,the elongate housing 112 may have a wall 152 with a wall thickness 154of about 1 millimeter or less. However, the elongate housing 112 is notlimited to any particular internal diameter 128 or dimension, or wallthickness 154. Further, the arbor 136 may be formed integrally with theelongate housing 112 or as a separate component that may be coupled tothe elongate housing 112. Without limitation, the arbor 136 may beformed of similar materials described above for the elongate housing112.

Referring to FIGS. 1A-1B, 3-4, and 6, the plurality of elongate cuttingmembers 114 may extend lengthwise at the distal end 122 of the elongatehousing 112 and may be positioned about the longitudinal axis 126 of theelongate housing 112. The elongate cutting members 114 may define asubstantially annular cutting surface 160 that may be adapted tocontract from a first diameter 162 or first dimension shown in FIG. 1Ato a second diameter 164 or second dimension shown in FIG. 1B. Thesecond diameter 164 or dimension may be less than the first diameter 162or dimension. Further, the first diameter 162 or dimension may besubstantially concentric to the second diameter 164 or dimension, andthe first diameter 162 or dimension may substantially correspond to theinternal diameter 128 of the elongate housing 112. The contraction ofthe annular cutting surface 160 from the first diameter 162 or dimensionto the second diameter 164 or dimension may define a tapered profile 168between the first diameter 162 or dimension and the second diameter 164or dimension. The tapered profile 168 may have any dimensions and rateof taper suitable for a particular grafting procedure. As describedbelow, the tapered profile 168 between the first diameter 162 ordimension and the second diameter 164 or dimension of the annularcutting surface 160 may provide the tapered graft tissue 108 with anexternal taper 172 or tapered sidewall. The external taper 172 ortapered sidewall of the tapered graft tissue 108 may substantiallycorrespond to the tapered profile 168 of the annular cutting surface 160along an entire length 174 of the tapered graft tissue 108. AlthoughFIGS. 1A-1B and 3-4 illustrate the annular cutting surface 160 as beingsubstantially annular or circular in shape, other shapes are possible.

Continuing with FIGS. 1A-1B and 3-4, the elongate cutting members 114may be formed, for example, integrally with the elongate housing 112 oras separate components coupled to the elongate housing 112. In someembodiments, the elongate housing 112 may have longitudinal cuts 180through the wall 152 of the elongate housing 112 that provide theelongate cutting members 114. The longitudinal cuts 180 may extendlengthwise along a portion of the distal end 122 of the elongate housing112 and about a circumference 182 or perimeter of the elongate housing112. In this manner, the longitudinal cuts 180 may provide the elongatecutting members 114 substantially as individual spring-like fingers atthe distal end 122 of the elongate housing 112. Each of the elongatecutting members 114 or spring-like fingers may have at least one cuttingtip 186. In a relaxed state as shown in FIG. 1B, the elongate cuttingmembers 114 may be spring biased inward toward the bore 124 of theelongate housing 112, positioning the annular cutting surface 160 in thesecond diameter 164. Further, the longitudinal cuts 180 may bepie-shaped as shown in FIG. 1A to permit clearance between each of theelongate cutting members 114 when the annular cutting surface 160 is inthe relaxed state and positioned in the second diameter 164.

The at least one cutting tip 186 associated with each of the elongatecutting members 114 may have any shape suitable for a particularapplication. For example, FIGS. 1A-1B depict an embodiment that may haveone pointed cutting tip 188 positioned at an end of each of the elongatecutting members 114. FIG. 3 depicts an embodiment that may have aplurality of pointed cutting tips 188 positioned at an end of each ofthe elongate cutting members 114 to provide saw-like serrations. FIG. 4depicts an embodiment that may have one flat cutting tip 190 positionedat an end of each of the elongate cutting members 114. The flat cuttingtip 190 may be smooth rather than pointed or serrated as shown in FIGS.1A-1B and 3, respectively.

Similar to the elongate housing 112, the first diameter 162 or dimensionof the annular cutting surface 160 may be, for example, between about 3millimeters to about 30 millimeters. The second diameter 164 ordimension of the annular cutting surface 160 may be any suitablediameter that is less than the first diameter 162. Further, the annularcutting surface 160 may have a thickness 192 of about 1.0 millimeter orless. However, the annular cutting surface 160 is not limited to anyparticular diameter or dimension, or thickness. Without limitation, theelongate cutting members 114 may be formed of similar materialsdescribed above for the elongate housing 112.

Referring to FIGS. 1A-4, the plunger 116 may have an external surface196 and a tissue contact surface 198 and may be slidably disposed in thebore 124 of the elongate housing 112. The plunger 116 may include aplunger guide rod 200 that may be adapted to extend from the plunger 116along the longitudinal axis 126 of the elongate housing 112. If theelongate housing 112 includes the optional arbor 136, in someembodiments, the aperture 146 in the arbor 136 may receive the plungerguide rod 200 to assist with guiding the plunger 116 in the bore 124 ofthe elongate housing 112. Further, the plunger guide rod 200 mayprotrude through the aperture 146 in the arbor 136 to the exterior ofthe elongate housing 112 to permit an operator to actuate the plunger116 from the exterior of the elongate housing 112.

In some embodiments, as shown in FIG. 4, the aperture 146 in the arbor136 may have internal threads 204 sized to receive an actuation rod 206having a corresponding externally threaded surface 208 and an end 210adapted to extend from the arbor 136 into the bore 124 of the elongatehousing 112. The end 210 of the actuation rod 206 may engage the plungerguide rod 200 in the bore 124 of the elongate housing 112 for actuatingthe plunger 116 from the exterior of the elongate housing 112 as theactuation rod 206 moves along the internal threads 204 of the arbor 136.

Referring to FIG. 11, in some illustrative embodiments, the plunger 116may be a plunger 116 a including a bearing (not shown) that may permitthe external surface 196 of the plunger 116 a to rotate about orrelative to the tissue contact surface 198 of the plunger 116 a. In theembodiment of FIG. 11, the tissue contact surface 198 may be a button199 that is rotatable on the bearing relative to the external surface196. In this manner, the tissue contact surface 198, or the button 199,may be substantially precluded from rotating relative to the taperedgraft tissue 108 during operation, permitting the tissue contact surface198, or the button 199, to remain substantially stationary relative tothe tapered graft tissue 108. For example, a circumference 197 of thetissue contact surface 198, or the button 199, may carry a bearing race(not shown) with the external surface 196 of the plunger 116 a beingdisposed about the bearing race and rotatable thereabout. Utilizing thebearing with the plunger 116 a may enhance the ability of the plunger116 a and cutting apparatus 106 to avoid damage to the tapered grafttissue 108.

Continuing with FIGS. 1A-4, when the annular cutting surface 160 has thefirst diameter 162 as shown in FIG. 1A, the elongate cutting members 114may be biased against the external surface 196 of the plunger 116 at thedistal end 122 of the elongate housing 112. When the plunger 116 ispositioned at the distal end 122 of the elongate housing 112, theelongate cutting members 114 may be moved away from the relaxed stateagainst a spring bias to position the annular cutting surface 160 in thefirst diameter 162. As shown in FIG. 1B, the plunger 116 may be slidabletoward the proximal end 120 of the elongate housing 112 to permit theannular cutting surface 160 to gradually contract to the second diameter164 and return to the relaxed state. In this manner, as describedfurther below, the annular cutting surface 160 may be adapted toautomatically contract from the first diameter 162 in FIG. 1A to thesecond diameter 164 in FIG. 1B as the annular cutting surface 160advances into an object and the object enters the bore 124 of theelongate housing 112, displacing the plunger 116 toward the proximal end120.

The plunger 116 and the plunger guide rod 200 may be formed integrallyor as separate components coupled to one another. Further, the plunger116 and the plunger guide rod 200 may be formed of any suitablematerial, such as, for example, stainless steel, titanium, or othersuitable material. The external surface 196 of the plunger 116 may haveany suitable size capable of fitting within the bore 124 of the elongatehousing 112 and moving the elongate cutting members 114 to position theannular cutting surface 160 in the first diameter 162. For example, anincrease in the external diameter of the plunger 116 may correspond toan increase in the first diameter 162 of the annular cutting surface160.

Referring to FIGS. 5A-5B, the system 102 may include a reamer 250 thatmay have an external cutting surface 252, a proximal end 254, and adistal end 256. The external cutting surface 252 of the reamer 250 mayhave a first diameter 262 or proximal diameter at the proximal end 254of the reamer 250 and a second diameter 264 or distal diameter at thedistal end 256 of the reamer 250. The first diameter 262 at the proximalend 254 of the reamer 250 may be larger than the second diameter 264 atthe distal end 256 of the reamer 250. The reamer 250 may be a taperedreamer and may define a tapered profile 268, or reamer taper, betweenthe first diameter 262 and the second diameter 264 of the reamer 250.The tapered profile 268 between the first diameter 262 and the seconddiameter 264 of the reamer 250 may substantially correspond to thetapered profile 168 between the first diameter 162 and the seconddiameter 164 of the annular cutting surface 160. The reamer 250 may havea reamer bore 270 or guide bore substantially aligned along a length 272and about a longitudinal axis 274 of the reamer 250 that may be adaptedto receive a reamer guide pin 276. The reamer 250 may be rotatable aboutthe reamer guide pin 276. The reamer 250 and the reamer guide pin 276may be formed of any suitable material, such as, for example, stainlesssteel or titanium.

Referring generally to FIGS. 1-6, in an illustrative embodiment ofoperation, an operator may position the plunger 116 at the distal end122 of the elongate housing 112 to position the annular cutting surface160 in the first diameter 162 as shown in FIG. 1A. Upon positioning theplunger 116 and the annular cutting surface 160 in the first diameter162, the operator may insert the annular cutting surface 160longitudinally into a donor tissue source (not shown). The annularcutting surface 160 may be advanced into the donor tissue source alongthe longitudinal axis 126 of the elongate housing 112 by pressing theannular cutting surface 160 into the donor tissue source with or withoutrotation of the annular cutting surface 160. Lubrication such as salinemay be applied to the plunger 116 and annular cutting surface 160 priorto and during insertion into the donor tissue source. Upon insertioninto the donor tissue source, the plunger 116 may move toward theproximal end 120 of the elongate housing 112 and be displaced by donortissue entering the bore 124 of the elongate housing 112 as the annularcutting surface 160 proceeds into the donor tissue source. The operatormay obtain the tapered graft tissue 108 having the external taper 172 bythe contracting action of the annular cutting surface 160 from the firstdiameter 162 to the second diameter 164 along the tapered profile 168 asthe plunger 116 is displaced toward the proximal end 120 of the elongatehousing 112. The tapered graft tissue 108 may be captured within thebore 124 of the elongate housing 112 when the annular cutting surface160 contracts to the second diameter 164. The tapered graft tissue 108may be extracted from the bore 124 of the elongate housing 112 byreturning the plunger 116 from the proximal end 120 of the elongatehousing 112 to the distal end 122 of the elongate housing 112. In someembodiments, the tapered graft tissue 108 may be extracted from anopening (not shown) at the proximal end 120 of the elongate housing 112.

Referring to FIG. 6, the tapered graft tissue 108 may include a graftinsertion end 280 and a graft exposed end 282 separated by the length174 of the tapered graft tissue 108. The tapered graft tissue 108 mayhave a first diameter 284, or exposed end diameter, at the graft exposedend 282 that is larger than a second diameter 286, or insertion enddiameter, at the graft insertion end 280. In some embodiments,substantially the entire length 174 between the first diameter 284 andthe second diameter 286 of the tapered graft tissue 108 may define theexternal taper 172 of the tapered graft tissue 108.

Referring to FIGS. 5A-6, the reamer 250 may be used for reaming orpreparing a tapered socket 302 in the tissue site 104 for receiving thetapered graft tissue 108. A pin insertion end 304 of the reamer guidepin 276 may be inserted into the tissue site 104 for adapting the tissuesite 104 to receive the tapered graft 108. A pin exposed end 306, oropposite end of the reamer guide pin 276 that opposes the pin insertionend 304, may be inserted into the reamer bore 270 of the reamer 250. Thereamer 250 may be rotated about the reamer guide pin 276 and advancedinto the tissue site 104 while being guided longitudinally along thelongitudinal axis 274 of the reamer 250 into the tissue site 104 by thereamer guide pin 276. Advancing the reamer 250 into the tissue site 104with the distal end 256 of the reamer 250 facing the tissue site 104 maycreate the tapered socket 302 as shown in FIG. 6.

The tapered socket 302 may define an internal taper 310 thatsubstantially corresponds to the external taper 172 of the tapered grafttissue 108 for receiving the tapered graft tissue 108 therein. Thus, thetapered graft tissue 108 may be adapted to self-align with the taperedsocket 302 when the graft insertion end 280 of the tapered graft tissue108 faces the tissue site 104 for insertion into the tapered socket 302.Further, the tapered graft tissue 108 and the tapered socket 302 mayeach have, for example, a conical, frustoconical, or pyramidal shape.After reaming or providing the tapered socket 302 in the tissue site104, insertion of the tapered graft tissue 108 into the tapered socket302 may take place. Prior to inserting the tapered graft tissue 108 intothe tapered socket 302, the tapered socket 302 may be finish sized toreceive the tapered graft tissue 108 with, for example, a tamp (notshown). The tamp may have an externally tapered profile substantiallycorresponding to the external taper 172 of the tapered graft tissue 108to provide final sizing of the tapered socket 302 for accepting thetapered graft tissue 108.

Experimental Results

Referring to FIGS. 7A-9C, fresh femoral condyles and humeral heads wereobtained from donor tissue sources. Cylindrical grafts 8 millimeters indiameter and 6 millimeters in height were created and implanted using aconventional system. Tapered grafts having an 8 millimeter firstdiameter at a top or exterior facing surface and a 6 millimeter heightwere implanted using a tapered graft system according to thisdisclosure. The cylindrical grafts and the tapered grafts were obtainedfrom and implanted into the same specimen. After surgical implantation,the cylindrical grafts and the tapered grafts were analyzed at day zeroto determine the immediate effect of graft implantation on cellviability and at day three to determine how changes in cell viabilitydevelop over time after implantation. For day zero testing, thecylindrical grafts and the tapered grafts were placed in a tissueculture media during processing for cell viability testing. For daythree testing, the cylindrical grafts and the tapered grafts were placedin the same tissue culture media with standard tissue culturesupplementation and stored at 37° Celsius with CO₂ supplementation. Forcell viability analysis, the cylindrical and the tapered grafts weresectioned and then assessed for cell viability by fluorescent microscopyusing the cell viability stains sytox blue (dead cell stain) and calceinAM (live cell stain). Images of each section of tissue were obtained,and the number of live and dead cells were determined using a validatedcell counting protocol. FIG. 7A depicts the cell viability for thecylindrical graft at day zero, and FIG. 7B depicts the cell viabilityfor the tapered graft at day zero. Further, FIG. 7C depicts the cellviability for the cylindrical graft at day three, and FIG. 7D depictsthe cell viability for the tapered graft at day three.

Percent cell viability was calculated by dividing the live cell count bythe total cell count and multiplying the result by 100 utilizing thefollowing formula: (live cell count/total cell count)*100. As shown inFIG. 7E, total cell viability did not differ significantly between thetapered and the cylindrical grafts at both day zero and day three afterimplantation. Such a result indicates that the graft type did notsignificantly affect total cell viability through day three of cultureafter graft insertion.

The area of superficial cell death and total tissue area were determinedon 4× images. The percent of superficial cell death area was determinedby dividing the area of superficial cell death by the total area of thetissue and multiplying the result by 100 utilizing the followingformula: (area of superficial cell death/total area of the tissue)*100.The area of superficial cell death is the ratio of the area of low cellviability in the superficial zone compared to the total area of thegrafted cartilage tissue. The superficial area of cell death wasdetermined by measuring the area of low cell viability from thesuperficial surface of the cartilage tissue down to the area of highcell viability deeper in the graft. FIG. 8A depicts the superficial areaof cell death for the cylindrical graft, and FIG. 8B depicts thesuperficial area of cell death for the tapered graft. As shown in FIG.8C, the tapered grafts had significantly less superficial cell deathcompared to the cylindrical grafts, suggesting that the tapered graftsystem is associated with significantly better superficial zonepreservation, which may correlate to improved outcomes.

For biomechanical testing, frozen hind limbs from donor test subjectswere obtained. Cylindrical grafts were created using a conventional 8millimeter OCA graft harvester. Tapered grafts were created using atapered graft system according to this disclosure having an 8 millimeterfirst diameter cutting surface. The cylindrical grafts and the taperedgrafts were trimmed to a depth of 6 millimeters. A 6 millimeter deepcylindrical hole was created for implantation of the cylindrical graftusing a conventional cylindrical cannulated reamer. Further, a 6millimeter deep tapered hole was created for implantation of the taperedgraft using a tapered cannulated reamer according to this disclosure.Each graft was manually positioned within the corresponding hole and aservo-hydraulic test machine equipped with a 880N load cell was used toseat each graft at a rate of 0.1 millimeters per second with force anddisplacement data being collected simultaneously at 100 Hertz. Insertionforce was plotted as a function of displacement and the area under thiscurve was calculated to yield insertion energy for each graft. FIG. 9Adepicts the insertion force for both the cylindrical graft and thetapered graft. FIG. 9B depicts the insertion energy for both thecylindrical graft and the tapered graft.

To measure extraction strength, the femur was rotated 180° and a guidepin was placed through the condyle until positioned flush against theopposite side of the graft. The above test machine was utilized to pusheach graft out, and the extraction strength was calculated for eachgraft. FIG. 9C depicts the extraction force for both the cylindricalgraft and the tapered graft. Statistically significant differences weredetermined using the students t-test or the rank sum test, depending ondata normality, with significance set at p<0.05 using Sigma Plot.

As shown in FIGS. 9A-9B, insertion force and energy required tooptimally seat the grafts were both significantly lower for the taperedgraft system compared to the cylindrical graft system in cadaverictissues. However, as shown in FIG. 9C, there was not a significantdifference between the two graft types for extraction strength requiredto extract the two types of grafts after insertion. These data indicatethat the tapered graft system according to this disclosure may decreasethe force and energy required to insert tapered grafts in a clinicallyrelevant manner. Further, the tapered graft system may decrease theassociated damage to the tapered graft without compromising stability ofthe tapered graft after insertion.

Additional testing was conducted using a tapered graft cutter having a20 millimeter first diameter cutting surface according to thisdisclosure to measure insertion energy and extraction force of graftscut from human femoral condyles. Cadaveric human femoral condyles wereacquired from tissue banks. Cylindrical grafts 20 millimeters indiameter and 6 millimeters in height were created and implanted using aconventional cylindrical graft system. Tapered grafts having a 20millimeter first diameter at a top or exterior facing surface and a 6millimeter height were created and implanted using a tapered graftsystem according to this disclosure. Each graft was trimmed to a depthof 6 millimeters prior to being implanted. A 6 millimeter deepcylindrical hole was created for implantation of the cylindrical graftusing a conventional cylindrical cannulated reamer. Further, a 6millimeter deep tapered hole was created for implantation of the taperedgraft using a tapered cannulated reamer according to this disclosure.Each graft was manually positioned within the corresponding hole and aservo-hydraulic test machine equipped with a 880N load cell was used toseat each graft. Insertion force was plotted as a function ofdisplacement and the area under this curve was calculated to yieldinsertion energy for each graft. FIG. 10A depicts the insertion energyfor both the cylindrical graft and the tapered graft. Additionally, theabove test machine was utilized to push each graft out as describedabove, and the extraction strength was calculated for each graft. FIG.108 depicts the extraction force for both the cylindrical graft and thetapered graft. Statistically significant differences were determinedusing the students t-test or the rank sum test, depending on datanormality, with significance set at p<0.05 using Sigma Plot.

Similar to the results above, both the insertion force and energyrequired to optimally seat the tapered grafts were significantly lowercompared to the conventional cylindrical grafts in cadaveric tissues.However, there was not a significant difference between the two grafttypes for extraction strength. Thus, this additional testing indicatesthat the larger 20 millimeter tapered graft system according to thisdisclosure may also decrease the force and energy required to inserttapered grafts in a clinically relevant manner. Further, the larger 20millimeter graft system may decrease the associated damage to thetapered graft without compromising the stability of the tapered graftafter insertion.

In summary, the testing shows that the tapered graft system according tothis disclosure was associated with significantly lower insertion forceand energy required to seat the tapered grafts compared to conventionalcylindrical grafts. Further, the tapered grafts exhibited similarextraction strength compared to conventional cylindrical grafts. Thus,the tapered graft system may allow surgeons to implant taperedosteochondral grafts, for example, with much less damage to the graftswhile still achieving the desired stability for graft healing andincorporation. Chondrocyte viability assessments from this study supportthis premise from biomechanical testing in that the tapered grafts wereassociated with significantly less cell death in the superficial zone ofthe cartilage. The preservation of superficial zone cartilage in thetapered grafts may be directly related to the lower force and energyrequired for insertion, and may result in improved clinical outcomes forgrafts implanted using the tapered graft system.

While this specification describes a number of non-limiting,illustrative embodiments, various modifications may be made withoutdeparting from the scope of this specification as defined by theappended claims. Further, any feature described in connection with anyone embodiment may also be applicable to any other embodiment. Thus,this specification contemplates that the various features of thedisclosed embodiments may be combined with one another.

1-16. (canceled)
 17. A method of grafting tissue at a tissue site,comprising: inserting a tapered graft tissue into a correspondingtapered socket at the tissue site.
 18. The method of claim 17, whereinthe tapered graft tissue is adapted to self-align with the taperedsocket at the tissue site.
 19. A method of grafting tissue at a tissuesite, comprising: obtaining a tapered graft tissue having an insertionend and an exposed end separated by a length, the tapered graft tissuehaving a first diameter at the exposed end that is larger than a seconddiameter at the insertion end, the length between the first diameter andthe second diameter defining an external taper; preparing a taperedsocket in the tissue site for receiving the tapered graft tissue, thetapered socket defining an internal taper that substantially correspondsto the external taper of the tapered graft tissue; and inserting thetapered graft tissue into the tapered socket.
 20. A method of graftingtissue at a tissue site, comprising: providing a cutting apparatus,comprising: an elongate housing having a proximal end, a distal end, anda bore defining a longitudinal axis, a plurality of elongate cuttingmembers extending lengthwise at the distal end of the elongate housingand positioned about the longitudinal axis of the elongate housing, theelongate cutting members defining an annular cutting surface adapted tocontract from a first diameter to a second diameter that is less thanthe first diameter thereby defining a tapered profile between the firstdiameter and the second diameter, and a plunger having an externalsurface slidably disposed in the bore of the elongate housing, whereinwhen the annular cutting surface has the first diameter the elongatecutting members are biased against the external surface of the plungerat the distal end of the elongate housing; positioning the plunger atthe distal end of the elongate housing to place the annular cuttingsurface in the first diameter; inserting the annular cutting surfacelongitudinally into a donor tissue source; displacing the plunger towardthe proximal end of the elongate housing with donor tissue entering thebore of the elongate housing as the annular cutting surface advancesinto the donor tissue source; obtaining a tapered graft tissue having anexternal taper by contracting the annular cutting surface from the firstdiameter to the second diameter along the tapered profile as the plungeris displaced; reaming a tapered socket in the tissue site for receivingthe tapered graft tissue, the tapered socket defining an internal taperthat substantially corresponds to the external taper of the taperedgraft tissue; and inserting the tapered graft tissue into the taperedsocket.
 21. (canceled)